1. Field of Invention
This invention relates to railroad car trucks and more particularly to frictional snubbing arrangements used to regulate movement between a bolster of the truck and its side frames.
2. Prior Art
Railroad car trucks are well known and are a high developed art form wherein for generations trucks have been continuously improved to accommodate increased loading, higher operating speeds and in more recent years, deteriorating road beds.
The modern day railroad car truck is often referred to as a three-piece truck comprising in part a pair of spaced side frames connected by a transversely positioned bolster having its ends resiliently supported by the side frames respectively. The bolster in turn supports a body of the railroad car which is cushioned by the resilient bolster side frame connection.
This cushioning is commonly provided by sets of coil springs and must be used with a dampening or snubbing device to regulate oscillating inherently produced with coil spring cushioning.
Early examples of dampening or snubbing devices used to regulate the resilient affected movements between a truck bolster and its side frames are disclosed in U.S. Pat. Nos. 2,378,414 and 2,378,415 wherein a vertical surface on a friction shoe carried by the bolster engages a side frame vertical wear surface positioned at each end of the bolster. A spring is used to urge the friction shoe outward to maintain the frictional engagement at a near constant level.
U.S. Pat. No. 2,720,172 discloses a further snubbing arrangement wherein each friction shoe is carried within a pocket formed at ends of the bolster and is forced upwardly and outwardly by inclined positioned coil springs. A vertical friction wall of the shoe engages a vertical wear plate carried by the side frame to dampen vertical movements cushioned by a set of load carrying coil springs.
A still further snubbing arrangement is disclosed in U.S. Pat. No. 2,953,955 wherein a set of friction shoes each having a central body portion and a pair of spaced triangular-shaped wings carried thereby is positioned in a like set of pockets in the truck bolster. The central body portion is hollow to contain a spring which forces the shoe upward against spaced inclined friction surfaces in the bolster pocket and in turn outwardly and against a vertical wear plate fastened to sides of a window in the side frame.
A last snubbing arrangement is disclosed by U.S. Pat. No. 3,805,707 and is pertinent in that it discloses a snubbing arrangement providing variable regulation in that the level of frictional engagement between friction shoes and side frame wear plates increases and decreases as a function of the compressive state of coil spring on which the friction shoe is carried.